Anders Logg wrote: > On Fri, Jan 29, 2010 at 10:31:05AM +0000, Garth N. Wells wrote: >> >> Anders Logg wrote: >>> On Fri, Jan 29, 2010 at 10:10:37AM +0000, Garth N. Wells wrote: >>> >>>>> Sub domains seem to be very different, but the other two cases just >>>>> seem to be a matter of some dofs being "active" and the other zeroed >>>>> out. This is what Marie suggested yesterday, that a restricted element >>>>> only considers a subset of the dofs of some given element. >>>>> >>>> Sounds good. >>>> >>>>> The thing I don't understand yet is the selection of which dofs should >>>>> be active. If we think of the case with restriction to facets, then >>>>> the element needs to be restricted to different facets depending on >>>>> which facet we are integrating over, or are we always mapping one >>>>> specific facet of the reference cell to the current facet? >>>>> >>>> It works the same way as the DG elements, just the internal dofs are >>>> thrown away, which is the latter if the above, right? >>>> >>>>> Say we have P1 elements in 2D which have 3 dofs. Then we could >>>>> restrict that element to the dofs on the first facet (facet 0). These >>>>> dofs are then labeled 1 and 2. But sometimes a facet in the mesh will >>>>> correspond to the edge between 0 and 1 or 0 and 2. >>>>> >>>> We don't restrict to individual facets, but to all facts of a cell. >>> That makes sense, but one thing still confuses me. Say that we have a >>> P1 element and restrict it to facets. Then all dofs are on the facets >>> so the result of the restriction is just a new P1 element. Same for P2 >>> where the result again is a new P2 element. >> Yes. >> >>> For P3, the result is P3 >>> element minus just one dof. >> Yes. >> >>> So does this make much difference for >>> other than very high degree elements? >>> >> It is only needed for k > 2. It's important because everything in >> FFC/UFL works for arbitrary orders. > > Yes, it should work for any order. I was just questioning the > usefulness of it if it results in standard P1 and P2 elements for > k = 1,2. > > Then I think I understand how it all works. > > But does the FFC demo make any sense?
We have a demo? > Could we simplify it so that it > just defines a finite element restricted to a facet and then some dS > integral? > Sounds good. > It currently breaks the code we added for RestrictedElement yesterday > because it has a complex nesting of restriction, then mixed with > another element and then restricted again. It looks like this is not > how you are using it in your solver. > The concept is very simple, so its implementation should be pretty simple too. Garth > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~ffc Post to : ffc@lists.launchpad.net Unsubscribe : https://launchpad.net/~ffc More help : https://help.launchpad.net/ListHelp
